1. Field of Invention
The present invention relates to detection and imaging devices and more particularly, is directed towards systems and methods for infrared detection and imaging.
2. Description of the Prior Art
U.S. Pat. No. 3,639,765 relates to thermal infrared (IR) imaging detectors utilizing thermally activated luminescent processes in a thin film of a microcrystalline phophor that is excited by ultraviolet or short wavelength visible radiation. An infrared image is converted into a visible image by thermal quenching or thermal enhancement of the visible luminescent intensity of different points in the film corresponding to elements of an infrared image focused into the film.
Such systems should outperform imaging instruments based on point detectors and mechanical scanners for objects having moderate to high contrast. In many applications, however, contrasts are low. Temperature differences of 1.degree. K in the vicinity of 300.degree. K have a contrast ratio of only about 1 percent. In order to resolve this difference with a good signal-to-noise ratio, the film should have a response uniformity of about 0.1 percent or better which is difficult to attain. If an image tube or solid state array is used for image presentation, its photosensitive surface should have at least the same uniformity as the luminescent film. Such requirements are beyond the state of the art.
The main contributions to the non-uniformities of an infrared imaging detector described in U.S. Pat. No. 3,639,765 are:
1. VARIATIONS IN THERMAL MASS BETWEEN DIFFERENT POINTS OF THE CONVERSION FILM;
2. DIFFERENCES IN LUMINESCENT EXCITATION EFFICIENCIES BETWEEN DIFFERENT POINTS OF THE CONVERSION FILM RESULTING FROM INHOMOGENEITIES IN THE LUMINESCENT LAYER;
3. VARIATIONS IN THE INTENSITIES OF THE LUMINESCENT EXCITATION RADIATION INCIDENT ON DIFFERENT POINTS OF THE CONVERSION FILM; AND
4. VARIATIONS IN RESPONSIVITY BETWEEN DIFFERENT POINTS OF THE PHOTOSENSITIVE SURFACE OF THE IMAGE TUBE (OR BETWEEN ELEMENTS OF A TWO-DIMENSIONAL ARRAY OF SOLID-STATE DETECTORS) USED FOR THE VISUAL DISPLAY OF THE INFRARED IMAGE.